Search results for "Fysiikka"
showing 10 items of 1348 documents
Massless positivity in graviton exchange
2021
We formulate Positivity Bounds for scattering amplitudes including exchange of massless particles. We generalize the standard construction through dispersion relations to include the presence of a branch cut along the real axis in the complex plane for the Maldestam variable $s$. In general, validity of these bounds require the cancellation of divergences in the forward limit of the amplitude, proportional to $t^{-1}$ and $\log(t)$. We show that this is possible in the case of gravitons if one assumes a Regge behavior of the amplitude at high energies below the Planck scale, as previously suggested in the literature, and that the concrete UV behaviour of the amplitude is uniquely determined…
Transport coefficients from in medium quarkonium dynamics
2019
The in medium dynamics of heavy particles are governed by transport coefficients. The heavy quark momentum diffusion coefficient, $\kappa$, is an object of special interest in the literature, but one which has proven notoriously difficult to estimate, despite the fact that it has been computed by weak-coupling methods at next-to-leading order accuracy, and by lattice simulations of the pure SU(3) gauge theory. Another coefficient, $\gamma$, has been recently identified. It can be understood as the dispersive counterpart of $\kappa$. Little is known about $\gamma$. Both $\kappa$ and $\gamma$ are, however, of foremost importance in heavy quarkonium physics as they entirely determine the in an…
Diffusion processes involving multiple conserved charges: a first study from kinetic theory and implications to the fluid-dynamical modeling of heavy…
2020
The bulk nuclear matter produced in heavy ion collisions carries a multitude of conserved quantum numbers: electric charge, baryon number, and strangeness. Therefore, the diffusion processes associated to these conserved charges cannot occur independently and must be described in terms of a set of coupled diffusion equations. This physics is implemented by replacing the traditional diffusion coefficients for each conserved charge by a diffusion coefficient matrix, which quantifies the coupling between the conserved quantum numbers. The diagonal coefficients of this matrix are the usual charge diffusion coefficients, while the off-diagonal entries describe the diffusive coupling of the charg…
Non-equilibrium dynamics of a scalar field with quantum backreaction
2021
We study the dynamical evolution of coupled one- and two-point functions of a scalar field in the 2PI framework at the Hartree approximation, including backreaction from out-of-equilibrium modes. We renormalize the 2PI equations of motion in an on-shell scheme in terms of physical parameters. We present the Hartree-resummed renormalized effective potential at finite temperature and critically discuss the role of the effective potential in a non-equilibrium system. We follow the decay and thermalization of a scalar field from an initial cold state with all energy stored in the potential, into a fully thermalized system with a finite temperature. We identify the non-perturbative processes of …
Space and Time Averaged Quantum Stress Tensor Fluctuations
2021
We extend previous work on the numerical diagonalization of quantum stress tensor operators in the Minkowski vacuum state, which considered operators averaged in a finite time interval, to operators averaged in a finite spacetime region. Since real experiments occur over finite volumes and durations, physically meaningful fluctuations may be obtained from stress tensor operators averaged by compactly supported sampling functions in space and time. The direct diagonalization, via a Bogoliubov transformation, gives the eigenvalues and the probabilities of measuring those eigenvalues in the vacuum state, from which the underlying probability distribution can be constructed. For the normal-orde…
Momentum anisotropy effects for quarkonium in a weakly coupled quark-gluon plasma below the melting temperature
2017
In the early stages of heavy-ion collisions, the hot QCD matter expands more longitudinally than transversely. This imbalance causes the system to become rapidly colder in the longitudinal direction and a local momentum anisotropy appears. In this paper, we study the heavy-quarkonium spectrum in the presence of a small plasma anisotropy. We work in the framework of pNRQCD at finite temperature. We inspect arrangements of non-relativistic and thermal scales complementary to those considered in the literature. In particular, we consider temperatures larger and Debye masses smaller than the binding energy, which is a temperature range relevant for presently running LHC experiments. In this set…
Massive Quarks at One Loop in the Dipole Picture of Deep Inelastic Scattering
2022
We calculate the light cone wave functions for a virtual photon to split into quark-antiquark states, including for the first time quark masses at one loop accuracy. These wave functions can be used to calculate cross sections for several precision probes of perturbative gluon saturation at the Electron-Ion Collider. Using these wave functions we derive, for the first time, the dipole picture DIS cross sections at one loop for longitudinal and transverse virtual photons including quark masses. The quark masses are renormalized in the pole mass scheme, satisfying constraints from the requirement of Lorentz invariance of the quark Dirac and Pauli form factors.
Production of ω mesons in pp collisions at √s = 7 TeV
2020
The invariant differential cross section of inclusive ω(782) meson production at midrapidity (|y|<0.5) in pp collisions at s√=7TeV was measured with the ALICE detector at the LHC over a transverse momentum range of 2<17GeV/c. The ω meson was reconstructed via its ω→π+π−π0 decay channel. The measured ω production cross section is compared to various calculations: PYTHIA 8.2 Monash 2013 describes the data, while PYTHIA 8.2 Tune 4C overestimates the data by about 50%. A recent NLO calculation, which includes a model describing the fragmentation of the whole vector-meson nonet, describes the data within uncertainties below 6GeV/c, while it overestimates the data by up to 50% for higher pT. The …
K∗(892)0 and φ(1020) production at midrapidity in pp collisions at √s = 8 TeV
2020
The production of K* (892)(0) and phi(1020) in pp collisions at root s = 8 TeV was measured by using Run 1 data collected by the ALICE collaboration at the CERN Large Hadron Collider (LHC). The P-T-differential yields d(2)N/dydp(T), in the range 0 < p(T) < 20 GeV/c for K*(0) and 0.4 < p(T) < 16 GeV/c for phi have been measured at midrapidity, vertical bar y vertical bar < 0.5. Moreover, improved measurements of the K*(0)(892) and phi (1020) at root s = 7 TeV are presented. The collision energy dependence of p(T) distributions, p(T)-integrated yields, and particle ratios in inelastic pp collisions are examined. The results are also compared with different collision systems. The values of the…
Production of charged pions, kaons, and (anti-)protons in Pb-Pb and inelastic pp collisions at √sNN = 5.02 TeV
2020
Midrapidity production of pi(+/-), K-+/-, and (p measured by the ALICE experiment at the CERN Large Hadron Collider, in Pb-Pb and inelastic pp collisions at √s(NN) = 5.02 TeV, is presented. The invariant yields are measured over a wide transverse momentum (p(T)) range from hundreds of MeV/c up to 20 GeV/c. The results in Pb-Pb collisions are presented as a function of the collision centrality, in the range 0-90%. The comparison of the P-T -integrated particle ratios, i.e., proton-to-pion (p/pi) and kaon-to-pion (K/pi) ratios, with similar measurements in Pb-Pb collisions at √s(NN) = 2.76 TeV show no significant energy dependence. Blast-wave fits of the p(T) spectra indicate that in the most…